Schoolgirl with an arm growing on her back...Doctors think it belonged to her unborn twin

Doctors were stunned after an 11-year-old schoolgirl was admitted to a hospital in China with a third arm sprouting out of her back.

The large mass was revealed to be part of an identical twin that had failed to develop and had been enveloped into the body of its sister. Further investigation found it consisted of a breast and an arm which included a shoulder blade and two fingers.

The case came to the attention of the medical world after it was highlighted by Professor Baogan Peng, of the General Hospital of Armed Police Force in Beijing.

Writing in the journalBMJ Case Reports, Prof Peng said: 'Based on physical examination and imaging findings, a diagnosis of fetus in fetu was made preoperatively.'

Fetus in fetu in an incredibly rare condition that affects only one in five million live births. It is a condition where the malformed foetus is found in the body of its twin. The foetus is found in the abdomen in 80 per cent of cases, although there have been reports of it occurring in the skull. However, this is the first time that is has been reported in the back.

The young patient also suffered from diastematomyelia, which is a congenital disorder in which the spinal cord is split.

Prof Peng, who is an expert in spinal surgery, said doctors successfully removed the parasitic twin, despite there being no clear way of separating them.

He added that a later analysis also found digestive tract lining in the tissue.

A back X-ray revealed abnormal curvatures of the spine (left). The case was reported by Professor Baogan Peng, of the General Hospital of Armed Police Force in Beijing

A CT scan of the girl's back. The arrow points towards evidence of a split spinal cord